feat: add three-way ad-hoc filters mode (extra_filters, root query, off)

[edspc]

Related issue: #633

Describe Your Changes

Replace the binary "Ad-hoc filters to root query" toggle with a three-option selector so users can disable automatic ad-hoc filter injection entirely. This prevents double-filtering when users manage ad-hoc values through Grafana variable interpolation and avoids silent empty results when filtering on pipe-transformed fields.

Checklist

The following checks are mandatory:

• My change adheres to VictoriaMetrics contributing guidelines.
• My change adheres to VictoriaMetrics development goals.

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Summary by cubic

Adds a three-option “Ad‑hoc filters” mode (Extra Filters, Root Query, Off) to replace the old toggle. This lets users disable automatic injection to avoid double-filtering and empty results when using pipes or variable interpolation. Related to #633.

• New Features

  • New adHocFiltersMode on queries with extraFilters, rootQuery, off; legacy isApplyExtraFiltersToRootQuery is still honored via resolveAdHocFiltersMode.
  • Query Editor now shows a radio selector and displays the selected mode in the collapsed summary.
  • Datasource behavior by mode:
    • Extra Filters: send as extra_filters.
    • Root Query: prepend to expr, clear extraFilters.
    • Off: do not inject ad‑hoc filters.
  • Tests updated/added for all modes and legacy fallback.

• Migration

  • Existing queries keep their behavior: default to Extra Filters unless the legacy flag is true (then Root Query).
  • If you manage filters via Grafana variables, set mode to Off to prevent duplicates.

^{Written for commit 911a4e0. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 4 files